Optical scanning system

Abstract

An optical scanning system is provided which includes a light source, a scanning deflector which deflects a bundle of rays emitted from the light source, and a scanning lens system which converges the deflected bundle of rays onto an image surface to form an image. The scanning lens system has at least two lenses, wherein the lens closest to the image surface is a meniscus lens with a surface which is convex in the main scanning direction facing the image surface. A surface of the meniscus lens nearest to the scanning deflector is a deformed toric surface which is convex in a sub scanning direction facing the scanning deflector. The sub scanning direction is normal to the main scanning direction. The convexed toric surface has a radius of curvature which is determined independently of a radius of curvature in the main scanning direction.

I claim: 
     
       1. An optical scanning system comprising: a light source;   a scanning deflector which deflects a bundle of rays emitted from said light source; and,   a scanning lens system which converges the deflected bundles of rays onto an image surface to form an image,   wherein said scanning lens system comprises at least two lenses, one of said lenses that is closest to said image surface being a meniscus convex lens that is disposed in a main scanning direction of said image surface, said meniscus convex lens having a surface which is convex in the main scanning direction facing said image surface,   and wherein the surface of said meniscus convex lens nearest to said scanning deflector is a deformed toric surface, said deformed toric surface being convex in a sub-scanning direction facing said scanning deflector, the sub-scanning direction being normal to the main scanning direction,   and further wherein said convex toric surface has a radius of curvature which is determined independently of a radius of curvature in the main scanning direction.   
     
     
       2. The optical scanning system of claim 1, wherein said scanning lens system comprises an imaging lens group which mainly functions to form an image, and a correcting lens group which mainly functions to correct an aberration on said image surface, and wherein said imaging lens group is located nearer to said scanning deflector than said correcting lens group, and further wherein said deformed toric surface is provided on said correcting lens group. 
     
     
       3. The optical scanning system of claim 2, wherein said imaging lens group comprises two imaging lenses. 
     
     
       4. The optical scanning system of claim 3, wherein said correcting lens group comprises a single lens. 
     
     
       5. The optical scanning system of claim 3, wherein said two imaging lenses of said imaging lens group have a positive power in the main scanning direction. 
     
     
       6. The optical scanning system of claim 5, wherein said two imaging lenses of said imaging lens group satisfy a following relationship;   0.6≦f/f1≦0.7     wherein "f1" designates a focal length of said lens of said imaging lens group that is located nearest to said scanning deflector in the main scanning direction, and "f" designates a focal length of said scanning lens system as a whole in the main scanning direction.   
     
     
       7. The optical scanning system of claim 1, wherein said scanning lens system consists of two imaging lenses. 
     
     
       8. The optical scanning system of claim 7, wherein said two imaging lenses satisfy a following relationship;   0.6≦f/f1≦0.7     wherein "f1" designates a focal length of said imaging lens that is located nearest to said scanning deflector in the main scanning direction, and "f" designates a focal length of said scanning lens system as a whole in the main scanning direction.   
     
     
       9. The optical scanning system of claim 1, wherein said meniscus lens having said deformed toric surface is made by plastic molding. 
     
     
       10. The optical scanning system of claim 1, further comprising: an anamorphic lens between said light source and said scanning deflector for converging said bundle of rays in the sub scanning direction, wherein said bundle of rays is made incident upon a deflecting surface of said scanning deflector.   
     
     
       11. An optical scanning system comprising a light source, a scanning deflector which deflects a bundle of rays emitted from said light source, and a scanning lens system which converges the deflected bundle of rays onto an image surface to form an image, said scanning lens system being comprised of at least two lenses which satisfy a following relationship;   0.6≦f/f1≦0.7     wherein "f1" designates a focal length of a lens of a scanning lens group that is located nearest to said scanning deflector in a main scanning direction, and wherein "f" designates a focal length of said scanning lens system as a whole in the main scanning direction.   
     
     
       12. The optical scanning system of claim 11, wherein a lens of a scanning lens group closest to said image surface is made of a meniscus lens with a convex surface that faces said image surface in the main scanning direction, wherein a surface of a meniscus lens nearest to said scanning deflector is a deformed toric surface which is convex in a sub scanning direction facing said scanning deflector, the sub scanning direction being normal to the main scanning direction, and further wherein said convexed toric surface has a radius of curvature which is determined independently of a radius of curvature in the main scanning direction. 
     
     
       13. An optical scanning system comprising: a light source;   a scanning deflector which deflects a bundle of rays emitted from said light source; and,   a scanning lens system which converges said deflected bundle of rays onto an image surface to form an image,   wherein said scanning lens system comprises at least two lenses, one of said lenses that is closest to said image surface being a meniscus convex lens that is disposed in a main scanning direction of said image surface, said meniscus convex lens having a surface which is convex in said main scanning direction facing said image surface,   wherein a surface of said meniscus convex lens nearest to said scanning deflector is a deformed toric surface which is convex in a sub-scanning direction facing said scanning deflector, said sub-scanning direction being normal to said main scanning direction, and   wherein a radius of curvature, in said sub-scanning direction, of said deformed toric surface increases from said optical axis towards a periphery of said meniscus convex lens, and centers of curvature in said sub-scanning direction are located along a curved line depending on an image height.